System and method for generation of synthesis gas from subterranean coal deposits via thermal decomposition of water by an electric torch

ABSTRACT

A system for gasification of coal deposits below the ground surface comprising an injection well assembly comprising one end positioned at the surface and the opposite end located adjacent or within the coal deposit; a production well assembly comprising one end positioned at the surface and the opposite end of the production well assembly located adjacent or within the coal deposit; a non-vertical reaction shaft assembly located adjacent or within the coal deposit, the non-vertical reaction comprising an injection end in communication with the end of the injection well assembly located adjacent or within the coal deposit and a production end in communication with the end of the production well assembly located adjacent or within the coal deposit; and an electric torch configured to move within the non-vertical reaction shaft assembly and create an oxidant and moderator downhole. A method for gasifying coal deposits is also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 12/056,960, filed Mar. 27, 2008, which claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 60/908,947, filed Mar. 29, 2007, the disclosure of each of which is hereby incorporated herein by reference in there entireties for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

BACKGROUND

1. Field of the Invention

The invention relates to underground gasification of coal deposits. More specifically, the invention relates generally to an apparatus and method for the generation of synthesis gas from subterranean deposits comprising coal using a directional, electric torch in a horizontal well-bore.

2. Background of the Invention

It is estimated that approximately 50% of existing coal is located too deep within the earth to be mined conventionally. Due to regulatory, safety, and environmental demands, some mining operators are being forced to close their mines, leading to a decrease in the productivity of traditional coal production in particular, and for coal use as an energy source in general. This has led to research on the feasibility of underground coal gasification, UCG.

Underground gasification has several inherent advantages over conventional mining, including the avoidance of safety and health hazards related to the underground mining of coal, avoidance of the environmental impact which occurs during the strip mining of coal. Additionally, UCG has demonstrated an ability to recover coal from seams unsuitable for conventional mining techniques.

In U.S. Pat. No. 4,776,638, Hahn describes a method for electro-thermal and electrochemical underground conversion of coal into oil and by-products. The method comprises inserting an underground probe into a bore hole until the probe is in close proximity with a coal seam. A mixture of air, steam, an electrolyte, and a suitable catalyst is supplied to the probe via a feed supply line, and the mixture is sprayed directly on the coal seam through a passage in a nozzle. Tunnels of limited horizontal reach, about 100 to 150 feet in length, are formed by advancing the probe away from the vertical well bore in a substantially horizontal direction into and through the coal seam during conversion. Products are removed from the same vertical well bore.

In U.S. Pat. No. 4,067,390, Camacho et al. describe an apparatus and method utilizing a plasma arc torch as heat source for recovering useful fuel products from in situ deposits of coal, tar sands, oil shale, and the like. When applied to a coal deposit, the plasma torch is lowered in a vertical shaft into the deposit and serves as a means for supplying heat to the coal and thereby stripping off the volatiles. The fixed carbon is subsequently gasified by reaction with steam that is externally supplied (i.e. from the surface) and sprayed into the devolatilized area and product gases are removed from the same vertical shaft. Umbilicals are provided for carrying electrical power, plasma gas, and cooling water. The plasma arc torch operates in a transferred mode wherein the arc is attached to an external forwardly-placed, axially aligned torch-mounted electrode. The externally-supplied heat energy of the plasma torch displaces the need for the combustion of a part of the deposit resource, which would result in unnecessary CO₂ production, which would in turn dilute the heating value of the product gases. Therefore, the plasma heat provides sufficient energy to take the place of the less desirable exothermic gasification reactions which would otherwise balance the heat requirements of the more desirable endothermic gasification reactions.

In U.S. Patent Application US-2008/0314593 A1, Vinegar discloses methods for recovery of fuel products from subterranean carbonaceous deposits. Related to Camacho, Vinegar discloses a method for the generation of heat energy delivered to a reaction zone which is used to replace the energy that would otherwise be generated by exothermic gasification reactions. Vinegar's heat generation is through the combustion of a fuel source that is supplied externally (i.e. from the surface) fuel source, in a burner, with an oxidant supplied externally (i.e. from the surface). Accordingly, this ‘heat source embodiment’ is comparable to Camacho's plasma (electric) heat source that is used to heat the coal formation.

Both Camacho and Vinegar disclose the use of distinct and separate umbilicals for an externally-supplied energy source (i.e. electricity in the case of Camacho and fuel in the case of Vinegar), an externally-supplied oxidant (in Vinegar), and an externally-supplied moderator (steam in the case of Camacho and steam or water in the case of Vinegar).

In U.S. Pat. No. 4,648,450, Gash et al. describe an underground coal gasification process containing a system of injection and production wells. The injection well is positioned at an angle with respect to horizontal of less than the angle of repose of loose coal and char for the particular coal seam, and the production well is positioned at an angle with respect to horizontal of greater than the angle of repose, but less than 90°. Each cavity in the operation can be individually valved to injection and production pipelines where a number of cavities are used in one coal seam. An oxygen-containing gas mixture is injected into the seam through the injection well and combustion products removed from the production well. An excess of oxygen-containing gas such as air or oxygen, or a mixture thereof, steam and oxygen, or carbon dioxide and oxygen is introduced to form a highly volatile and combustible combination within the coal deposit. This is ignited by electrical means or by the introduction of pyrophoric mixtures.

In U.S. Pat. No. 4,662,443, Puri describes use of an air-blown underground coal gasification plant to produce low-BTU gas and an oxygen-blown plant for the production of product gas from which synthetic natural gas may be produced.

U.S. Pat. No. 4,422,505 to Collins describes a method for gasifying subterranean coal deposits by positioning a cased injection well to extend from the surface into the coal deposit with the injection well extending horizontally through the lower portion of the coal deposit with the horizontal portion of the well being cased with a perforated casing; positioning an injection tubing within the injection well; positioning a production well to extend from the surface to a point near the lower end of the injection well; igniting the coal deposit; gasifying a portion of the coal deposit between the bottom of the production well and the lower end of the injection tubing well by injecting a free-oxygen containing gas into the coal deposit through the injection tubing and recovering product gases through the production well and thereafter gasifying a second portion of the coal deposit by withdrawing the injection tubing a selected distance and thereafter injecting free-oxygen containing gas into the coal deposit and recovering product gases from the production well. By the process of this invention, the use of vertical gas injection wells is eliminated. The invention purports to utilize no coolant. Desirably, a high temperature alloy (e.g., stainless steel) injection nozzle is positioned on the lower end of the injection tubing.

High-temperature steel for the injection nozzle for the oxidant is also described in the draft research report “Best Practices in Underground Coal Gasification” by Burton et al, Lawrence Livermore National Laboratory, 2006. Oxidant is delivered to the reaction point by coiled tubing, which itself is encased by a concentric conduit in the form of a well casing. The casing is preferably constructed of a consumable material, such that the casing burns away as the oxidant nozzle is refracted. This method is a basis for the Controlled-Refraction Injection-Point (CRIP).

Little progress has been made in processes for in situ gasification of coal in the past two decades primarily due to a lack of economic incentives. There remains the risk of potential environmental contamination of near-surface potable aquifers, due to working within proximity to the surface. There remain challenging technical problems such as the inability to adequately control the process. One particular technical problem is the ability to achieve high reaction temperatures at low cavity pressures, and thus the production of product gas of desired quality and quantity.

Another particular technical problem is the ability to operate at high cavity pressure as would be found in a deeper coal deposit. A third particular technical problem is the ability to control the in-leakage of ground water into the cavity. A fourth particular technical problem is delivery of gaseous oxidant at high pressure to a deep coal deposit.

Accordingly, there remains a need for a safe and effective system and method for generating synthesis gas from deeper coal deposits. In certain embodiments, the system and method should reduce the number of injection and/or production wells, thus minimizing surface disturbance, product leakage, and other negative environmental impact, should also allow for much deeper extraction of coal deposits, and/or should allow for higher reaction temperatures and pressures, and the control of these and other process parameters.

SUMMARY

Certain embodiments of the invention relate to a system for the gasification of a coal deposit located below the ground surface, the system comprising: at least one injection well assembly comprising one end positioned at the ground surface and the opposite end of the injection well assembly located adjacent or within the coal deposit; at least one production well assembly comprising one end positioned at the ground surface and the opposite end of the production well assembly located adjacent or within the coal deposit; at least one non-vertical reaction shaft assembly located adjacent or within the coal deposit a distance below ground surface, the at least one non-vertical reaction shaft having a length and comprising an injection end in communication with the end of the injection well assembly located adjacent or within the coal deposit and a production end in communication with the end of the production well assembly located adjacent or within the coal deposit; and at least one electric torch configured to move within the non-vertical reaction shaft assembly and create an oxidant and moderator downhole.

The coal deposit may comprise at least one selected from the group consisting of peat, lignite, other coals, kerogen-infused coals, methane-infused coals, and combinations thereof. The coal deposit may comprise at least one selected from the group consisting of peat, lignite, sub bituminous coal, bituminous coal, anthracite, and combinations thereof.

In certain embodiments, the at least one injection well assembly is within 15 degrees of vertical. In certain embodiments, the non-vertical reaction shaft assembly diverges from horizontal by less than about 30 degrees. In embodiments, the non-vertical reaction shaft assembly diverges from vertical by more than 15 degrees.

The electric torch may comprise a plasma arc torch. In embodiments, the electric torch utilizes steam as the plasma gas. In some embodiments, the at least one electric torch comprises at least two discharge heads. In embodiments, the electric torch comprises two opposed discharge heads, in which the directional opposition is not parallel to centerline of the wellbore. The electric torch may be a mobile directional electric device, operable to direct (i.e. vector) the discharge heads off-axis. In embodiments, the electric torch comprises one or more directional jets which may be actively or passively vectored to shape a reaction cavity. In embodiments, the electric torch comprises two or more directional jets, of which one jet is substantially concentric with the well-bore. The electric torch can be operable to separate positively charged species from negatively charged species, to separate oxidizers from reducers or both and to expel separate jets thereof.

In some embodiments, the non-vertical reaction shaft is at least partially lined by a thermally-consumable casing material. In embodiments, the non-vertical reaction shaft is at least partially water-cooled. In some embodiments, the distance below ground surface is greater than about 1,000 feet (304.8 m). In embodiments, the distance below ground surface is greater than about 3,000 feet (914.4 m). In certain embodiments, the distance below ground surface is in the range of from about 3,000 feet (914.4 m) to about 8,000 feet (2438.4 m) and beyond. The length of the at least one non-vertical reaction shaft may be greater than 1,000 feet (304.8 m). In some embodiments, the length of the at least one non-vertical reaction shaft is in the range of from about 10,000 feet (3048.0 m) to 15,000 feet (4572 m) and beyond.

In certain embodiments, the only fluid inlet into the system is one or more inlets for water. In embodiments, no primarily gaseous feed is provided to the electric torch following startup. In embodiments, no primarily gaseous feed is introduced to the electric torch either during startup or thereafter.

The production well assembly may further comprise at least one product casing, at least one steam jacket casing surrounding at least a portion of the at least one product casing, and at least one external water jacket casing surrounding at least a portion of the at least one steam jacket casing, wherein the external water jacket casing comprises an inlet for water and wherein the steam jacket casing comprises an outlet for steam and wherein the product casing transfers product gasification gas from the non-vertical reaction shaft assembly to the surface. At least one of the at least one steam jacket casing and the at least one product casing may be capable of expanding independently and/or at different rates of thermal expansion as compared to the at least one external water jacket casing. In certain embodiments, at least one casing selected from the at least one product casing and the at least one steam jacket casing comprises spacers (known in the art as ‘centralizers’), whereby the at least one casing remains substantially concentric with the at least one external water jacket casing during gasification of the coal deposit.

Certain embodiments of the invention also relate to a method for gasifying a coal deposit located below the ground surface, the method comprising: positioning an electric torch comprising at least one discharge head within a non-vertical reaction shaft assembly having a length, an injection end and a production end and wherein the non-vertical reaction shaft assembly is positioned at least partially within the coal deposit a distance of preferably at least 1,000 feet (304.8 m) below ground; and internally creating, with the electric torch, an oxidant and a moderator from an externally-supplied liquid source, whereby at least a portion of the coal deposit is gasified to create a reaction cavity, wherein the electric torch is operated at a temperature. In embodiments, the coal deposit comprises at least one selected from the group consisting of peat, lignite, sub bituminous coal, bituminous coal, anthracite, and combinations thereof.

In certain embodiments, the electric torch is attached to one end of each of at least one retaining cables whereby each of the at least one retaining cables extends from the electric torch through an injection well to the ground surface; and wherein the production end of the non-vertical reaction shaft assembly is in communication with a below-ground end of a production well, and wherein the injection well comprises one end in communication with the ground surface and one end in communication with the injection end of the non-vertical reaction shaft assembly. The at least one retaining cable may surround or comprise one or more selected from insulated electrical conductors, grounds, and combinations thereof.

In certain embodiments, the production well further comprises at least one product casing adapted to transfer product gasification gas from the non-vertical reaction shaft assembly to the surface, at least one steam jacket casing surrounding at least a portion of the at least one product casing, and at least one external water jacket casing surrounding at least a portion of the at least one steam jacket casing; and wherein the method further comprises injecting water into at least one inlet of the external water jacket casing and extracting steam from at least one outlet of the steam jacket casing. At least one of the at least one steam jacket casing and the at least one product casing may be capable of expanding independently and/or at a different rate of thermal expansion as compared to the at least one external water jacket casing. At least one casing selected from the at least one product casing and the at least one steam jacket casing may comprise spacers, whereby the at least one casing remains substantially concentric with the at least one external water jacket casing during gasification of the coal deposit.

In certain embodiments of the method for gasifying a coal deposit, the non-vertical reaction shaft assembly diverges from vertical by more than 15 degrees. The electric torch may operate with steam as plasma gas. The electric torch may comprise at least two discharge heads. The electric torch may comprise directional discharge heads. The electric torch may comprise one or more directional jets which may be actively or passively vectored to shape the reaction cavity. In embodiments, the method further comprises operating the electric torch to separate positively charged species from negatively charged species or to separate oxidizers from reducers and to expel separate directional jets thereof.

In certain embodiments, the distance below ground surface is greater than about 3,000 feet (914.4 m). In some embodiments, the distance below ground surface is in the range of from about 3,000 feet (914.4 m) to about 8,000 feet (2438.4 m) or beyond. In some embodiments, the length of the horizontal reaction shaft is greater than 1,000 feet (304.8 m). In some embodiments, the length of the non-vertical reaction shaft is in the range of from about 10,000 feet (3048 m) to 15,000 feet (4572.0 m) or beyond.

The method for gasifying a coal deposit may further comprise injecting water as coolant, reactant, and/or moderator during gasification, whereby the mobile electric torch produces steam and oxygen for its operation. In some embodiments, water is the only fluid injected into the electric torch and the non-vertical reaction shaft assembly following startup.

The temperature of the centerline of the discharge gas may be greater than about 2,000° F. (1,093° C.). In some embodiments, the discharge gas is an electric arc and the temperature of the centerline of the electric arc is greater than about 8,000° F. (4426° C.).

The method may further comprise repositioning the electric torch along the non-vertical reaction shaft whereby another portion of the coal deposit may be gasified. Repositioning the electric torch may comprise positioning the electric torch closer to the injection end of the non-vertical reaction shaft assembly.

The method for gasifying a coal deposit may further comprise collecting product gases that exit the production well at the ground surface. The product gas may be monitored to determine at least one selected from the group consisting of gas temperature, BTU value, gas content, water content, opacity (ash content), and mass flow rate of the product gas. At least one operating parameter may be adjusted in response to the monitoring. The at least one operating parameter may be selected from injection rate of fluid provided to the electric torch, electric torch power, positioning of the electric torch within the non-vertical reaction shaft and combinations thereof.

The disclosed method for gasifying a coal deposit may be utilized to continuously gasify portions of the coal deposit along substantially the entire length of the non-vertical reaction shaft assembly. In some embodiments, the method further comprises operating the mobile electric torch only during off-peak electrical demand periods, storing up heat in the reaction cavity until another non-peak electrical demand period.

Also disclosed is a method for gasifying a coal deposit located below the ground surface, the method comprising: positioning a plasma device comprising a discharge head within a horizontal reaction shaft assembly located at least 1,000 feet (304.8 m) below ground, the horizontal reaction shaft assembly having a length, an injection end, and a production end, and wherein the horizontal reaction shaft assembly is positioned at least partially within the coal deposit; and creating an oxidant at a temperature with the plasma torch whereby at least a portion of the coal deposit is gasified creating a reaction cavity, wherein the only fluid introduced into the horizontal reaction shaft assembly during substantially all of the gasification is water.

Embodiments of the invention comprise a combination of features and advantages which enable them to overcome various problems of prior devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention, and by referring to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more detailed description of embodiments of the invention, reference will now be made to the accompanying drawings, wherein:

FIG. 1 is a schematic of an embodiment of a gasification system in accordance with the invention.

FIG. 2 is a schematic of another embodiment of a gasification system in accordance with the invention.

FIG. 3 a is a schematic of an injection well assembly according to an embodiment of the invention.

FIG. 3 b is a schematic of an umbilical according to an embodiment of the invention.

FIG. 4 is a vertical section view of a suitable production well assembly according to an embodiment of the invention

FIG. 5 a is a schematic of an electric torch during use in gasification of a coal deposit according to an embodiment of the invention.

FIG. 5 b is a schematic of an electric torch during use in gasification of a coal deposit according to another embodiment of the invention.

FIG. 6 is a schematic of electric torch according to another embodiment of the invention.

FIG. 7 is a plan view one of several possible arrays for the positioning of the injection well assembly, horizontal reaction shaft, product gallery, and production well assembly, in a typical coal deposit to be gasified.

NOTATION AND NOMENCLATURE

The terms “non-vertical reaction shaft” and “horizontal reaction shaft” are used to refer to shafts which deviate by at least 15 degrees from vertical. “Horizontal” reaction shaft assembly 20 may be referred to herein as a “horizontal” shaft although it may deviate by up to about 85 degrees from horizontal.

The term “mobile” as used herein with respect to “mobile electric torch” is used to indicate that the electric device (e.g., plasma torch) is positionable through vertical injection well assembly 15 and into the non-vertical reaction shaft assembly (horizontal reaction shaft assembly) 20 and may be repositioned therein.

The term “directional” as used herein with respect to “mobile directional electric torch” is used to indicate that, in embodiments, the discharge 31 of the electric torch/device 30 may be directed about the axis of the electric torch 30 such that the discharge may be directed to substantially ungasified portions of the coal deposit.

The term “reaction zone” is used herein to refer to the area in which gasification reactions are occurring. The term “reaction cavity” is used to refer to the cavity 14 produced by the gasification reactions.

DETAILED DESCRIPTION

The system and method of this disclosure provide a means for the recovery of energy products from underground coal seams and other coal matter. Embodiments of the systems and methods for the gasification of coal or another coal deposit in situ comprise an electric torch, which may be used to add heat to a reaction zone, produce from the cooling water the required steam which serves as moderator, and/or further provide oxygen via the dissociation of steam which serves as oxidant for the reactions.

Methods discussed herein are particularly advantageous where the carbon resource is deep. In situ gasification is generally favored by depth and high pressure. The pressure at a depth of 4,000 feet (1,219 m) may be, for example, greater than about 2000 psia (13.8 MPa). However, delivering from the surface the steam moderator and oxidant at these depths and pressures, as well as controlling the reaction rate and temperature, represent unique challenges, which have not been overcome in the prior art, but have been addressed via certain systems and methods of this disclosure.

These challenges have been addressed, inter alia by utilizing an electrically powered, underground coal gasifier that creates its own steam and oxygen at the point of reaction from injected water. The torch method disclosed herein provides an increase in reaction temperature, pressure, depth, flow rate, capacity and/or cleanliness as compared to current Underground Coal Gasification (UCG) methods. The torch method may increase reaction temperature, pressure, depth, flow rate, capacity and/or cleanliness by a factor of at least two, and perhaps more than ten, compared to current UCG methods. The only fluid inlet to the electric torch may comprise one or more inlets for liquid. The liquid may be water and/or carbon dioxide. The liquid may be a solution of water containing dissolved oxidants such as hydrogen peroxide, dissolved oxygen gas, and dissolved chemical oxidants. The electric torch produces its own oxidizing fluid (i.e. oxidant) by the high temperature thermal decomposition of water and/or carbon dioxide. The electric torch requires no external gaseous moderator, but rather produces its own moderator (i.e. steam) by the heat generated in the process of creating the oxidant (i.e. oxygen) from the single fluid source (i.e. water or liquid carbon dioxide). The electric torch transfers electric energy to a surface-supplied fluid (i.e. liquid water or liquid carbon dioxide) to produce an oxidant and a gaseous moderator. The electric torch indirectly heats a coal formation by generating oxidant, which in turn produces heat via exothermic reactions with the in-situ formation fuel. No externally supplied (i.e. from the surface) gaseous oxidant is required by the electric torch, in embodiments. No externally supplied (i.e. from the surface) gaseous moderator is required by the electric torch, in embodiments. In embodiments, no primarily gas feed is introduced to the electric torch following startup. In embodiments, no primarily gas feed is introduced to the torch.

In contrast to conventional underground gasification systems and method which generally utilize a heat source to directly heat a formation, the disclosed system and method employ a heat source to heat a surface-supplied fluid (e.g. water). The heat is used to create steam moderator (from the surface-supplied fluid) and to thermally decompose the fluid to provide oxidant (i.e. oxygen) and optionally hydrogen.

The coal deposit to be gasified may comprise any suitable carbon resource. Preferred feedstock is a ubiquitous source that is not currently in high demand. A preferred ultra-low cost (near-zero value) feedstock is stranded, deep coal, deeper than coal that might otherwise be exploited by coal-bed methane recovery. Because the system and method of this disclosure may be utilized to obtain energy from deep coal deposits, new reserves, which have previously remained untapped by previous methodologies having significantly less capability, become viable sources of energy via this invention.

The disclosed method and system preferably eliminate the traditional pressure-vessel style of gasifier and essentially turn the gasifier inside-out, bringing the gasifier to the coal rather than vice versa. Traditional gasifiers are used in combination with an associated oxygen plant. The utilization of electric torch and very high temperature steam via this disclosure eliminates the need for an associated oxygen plant for gasification.

The system and method provide a safer and more environmental-friendly method of extracting energy from coal deposits as compared with traditional mining methods, for example compared with coal mining Environmental, Health, and Safety (EHS) guidelines. Embodiments of the system and method create a steam-based plasma in a deep coal seam, converting water into ultra-high temperature steam (plus hydrogen and oxygen) for the gasification of the coal, and subsequent returning product gases to the surface.

FIG. 1 is a schematic of a gasification system 10 according to an embodiment of the invention. FIG. 2 is a schematic of another embodiment of a gasification system 10 according to an embodiment of the invention. Gasification system 10 comprises an injection well assembly 15, a non-vertical or horizontal reaction shaft assembly 20, a production well assembly 42, and at least one electric torch 30.

Referring to the drawings and particularly to FIGS. 1 and 2, a vertical section of a typical coal deposit is shown wherein carbonaceous deposits or coal seams 11 are separated by relatively narrow non-carbonaceous deposit layers or non-coal layers 12 of shale, sandstone, limestone, or the like. The carbonaceous deposit or coal seams 11 may comprise coal, including, but not limited to, peat, lignite, sub bituminous coal, bituminous coal, anthracite, and combinations thereof. Carbonaceous deposit 11 may comprise kerogen, shale oil, bitumen, tars, tar sands and combinations thereof. By way of non-limiting example, suitable coal is sub-bituminous coal having a heating value of 9,190 BTU/lb (4,398 kJ/kg), on an as-received basis, a moisture content of about 24.1% by weight, an ash content of about 5.7% by weight, and a sulfur content of about 0.4% by weight. The coal seam 11 to be gasified may be infused with another carbonaceous fuel source, for example kerogen or methane.

Although it is to be understood that carbonaceous deposit 11 is not to be limited to coal, the following description of the system and method will be made with reference to carbonaceous deposits comprising coal. Above coal seams 11 and non-coal layers 12 is an overburden 13 comprising interspersed layers of earth, sand, shale, sandstone, limestone, saline aquifers, or the like.

System 10 comprises injection well assembly 15. Injection well assembly 15 is preferably positioned so that one topside end of injection well assembly 15 is at or above the earth surface 51, and the other below-ground end of injection well assembly 15 is positioned within the coal seam 11 to be gasified. In embodiments, injection well assembly 15 is substantially vertical. In other embodiments, injection well assembly 15 is not vertical. FIG. 3 is a schematic of an injection well assembly 15 according to an embodiment of the invention. As shown in FIG. 3, injection well assembly 15 comprises injection well casing 21. Typically, injection well casing 21 lines the entirety of injection well assembly 15.

The below-ground end of injection well assembly 15 is in communication with at least one horizontal reaction shaft assembly 20. As best illustrated in FIG. 2, in embodiments, injection well assembly 15 extends from surface 51, through overburden 13, and has a below-ground end in communication with several horizontal reaction shafts that follow the coal seam deposits 11 and that are more or less parallel to the coal seam(s) 11. Injection well assembly 15 may be a centralized injection well, with horizontal reaction shaft assemblies 20 proceeding in a radial direction therefrom.

While it is known in the art that the coal deposit can be more than 3,000 feet below the surface, it is also known that the permeability of coals at these depths is very low. For this reason, coal-bed methane recovery is generally not practiced much deeper than 3,000 to 3,500 feet. In UCG, coal permeability (the ability of gases to enter into the coal through cracks and fissures), and porosity (coal char surface area), would be insufficient at these depths to allow for reaction of cavity gases with the solid coal surface. Such reactions of gasses with the solid surface are known as heterogeneous reactions. Further, some higher-rank coal is known to swell when heated. This swelling exacerbates the low porosity or permeability of the coal. Deeper coal may typically be of higher rank (bituminous or greater) due to increased heat and pressure on the coal. Therefore, underground coal gasification is typically not practiced at depths, greater than 3,000 feet. The disclosed system and method allow for operation at depths greater than 3,000 feet, without injection of oxidant gas (e.g. concentrated oxygen) from the surface.

Deeper coals with low permeability and or porosity may conventionally require active erosion of the coal face in order to complete the heterogeneous reactions quickly. Contrarily, the disclosed electric torch 30 is designed to emit one or more high-velocity jets of oxidant and/or moderator. The jet is operable to cut the solid coal face by creating gaseous erosion and turbulence in the horizontal direction, perpendicular to the cavity center-line, at what is called the flame front.

As shown in FIG. 1, injection well assembly 15 may extend into the earth a depth 16 of greater than about 1,000 feet (304.8 m). Injection well shaft assembly 15 may extend into the earth a depth 16 of greater than about 3,000 feet (914 m). In preferred embodiments, injection well shaft assembly 15 extends into the earth a depth 16 in the range of from about 3,000 feet (914 m) to about 12,000 feet (3,656 m). In embodiments, injection well shaft assembly 15 extends into the earth a depth 16 in the range of from about 3,000 feet (914 m) to about 12,000 feet (3,657 m).

As mentioned hereinabove, gasification system 10 comprises at least one horizontal reaction shaft assembly 20. Preferably, horizontal reaction shaft assembly 20 is substantially parallel with the coal seam 11 to be gasified. As shown schematically in FIGS. 1 and 2, at least a portion of horizontal reaction shaft assembly 20 is positioned within coal seam 11 to be gasified. Preferably, substantially all of horizontal reaction shaft assembly 20 is positioned within coal deposit 11 to be gasified. Horizontal reaction shaft assembly 20 will usually be more-or-less horizontal, but may diverge from horizontal up to 85 degrees. For example, in the case of steeply dipping beds, the divergence of horizontal reaction shaft assembly 20 from horizontal may approach 75 degrees or more. Horizontal reaction shaft assembly 20 comprises an injection end positioned in proximity to the below-ground end of injection well assembly 15 and a production end in proximity with the below-ground end of production well assembly 42. The term “injection end” is used to signify that the injection end of horizontal reaction shaft assembly 20 is closer to the injection well assembly 15 than to production well assembly 42, while the term “production end” is used to signify that the production end of horizontal reaction shaft assembly 20 is closer to production well assembly 42 than to injection well assembly 15.

The distance 17 between injection well shaft assembly 15 and production well assembly 42 that is fluidly connected via horizontal reaction shaft assembly 20 may be greater than about 1,000 feet (304 m). In embodiments, distance 17 may be 3,000 feet (914.4 m). In embodiments, distance 17 may be greater than about 5,000 feet (1,524 m). In embodiments, distance 17 may be greater than about 10,000 feet (3,048 m). Alternatively, distance 17 may be greater than about 15,000 feet (4,572 m) or more. In certain embodiments, distance 17 is in the range of from about 10,000 feet to about 15,000 feet (3,048 m to 4,572 m).

Referring now to FIG. 1, radius injection bore 22 may provide mechanical communication between injection well assembly 15 and the injection end of horizontal reaction shaft assembly 20, as known to those of skill in the art. Horizontal reaction shaft assembly 20 is preferably lined with consumable casing 18, which may line all or a portion of assembly 20. Consumable casing 18 is constructed of a material such that the heat created by the electric torch 30 and the gasification reactions erodes the portion of consumable casing 18 within reaction zone 32, thus creating reaction cavity 14 during gasification. The production end of horizontal reaction shaft assembly 20 is positioned within coal deposit 11 in proximity with a below-ground end of production well assembly 42. Using a single injection well assembly 15 and a single production well assembly 42 enables the creation of many reaction cavities 14, minimizing both surface and below-grade environmental impact. As seen in FIG. 7 and discussed in more detail hereinbelow, multiple reaction cavities 14 may be in communication with a common product gallery 40, whereby product gas may exit one or more production well assemblies 42.

Other lines may be situated within consumable casing 18. For example, a line for a start-up gas may be positioned within consumable casing 18. Such a start-up gas may be useful, for example, to initiate the electric torch in an underwater environment.

Still referring to FIG. 1, gasification system 10 comprises production well assembly 42. Production well assembly 42 comprises a topside end and a below-ground end. Production well assembly 42 typically comprises product casing 43, which may line at least a portion of the production well assembly 42 from within coal seam 11 to the surface 51. The topside end, or “well-head,” of production well assembly 42 comprises an outlet for product gas 49. The below-ground end of production well assembly 42 is positioned within coal deposit 11 and is in communication with the production end of horizontal reaction shaft assembly 20.

Turning to FIG. 4, a vertical section view of a suitable production well assembly 42 according to an embodiment of the invention is showing. In this embodiment, production well assembly 42 is a steam-generating production well. Because of the high temperature of the product gases 49 a which enter product casing 43, production well assembly 42 may comprise cooling jackets such as steam jacket casing 44 and water jacket casing 45. Production well assembly 42 preferably comprises water injection line 46 through which cooling water 57 may be supplied at high pressure. Cooling water 57 will absorb heat from steam jacket casing 44 and product gases 49 a, eventually flashing to high pressure steam. This serves to cool the reaction products 49 a in product casing 43. Steam jacket casing 44 comprises at least one outlet 60 for high pressure steam 41. High pressure steam 41 may be used for power production or other beneficial use. For example, gasification system 10 may further comprise steam turbine/condenser 53 (see FIG. 1) which may serve to convert a portion of high pressure steam 41 into electricity. At least a portion of the electricity 54 produced may be used to provide power to electric torch 30.

In embodiments, the hot product gases are isolated from the relatively cool outer well casing in contact with the soil/rock. In embodiments, the raising of steam is used to benefit as the preferred cooling method. In embodiments, the high pressure of the steam casing is such that the differential pressure across the product casing is minimized, allowing for a thinner, more economical, and/or more flexible casing. In embodiments, high-pressure steam is created via the weight of the head of liquid water in the outer casing. In embodiments, water sprayed as a coolant at the bottom of the casing assembly is utilized to provide product gas water quench, chemical quench, and/or particulate wash. In embodiments, the system and method utilize concentric casings configured to support each other while maintaining the ability to expand thermally at different rates of growth. In embodiments, the system and method incorporate at least one multi-concentric production well for obtaining the hot, high-pressure product gases.

Due to differences in thermal expansion of the concentric casings including product casing 43, steam jacket casing 44 and water jacket casing 45, production well assembly 42 may further comprise slip joints such as topside slip joint(s) 47 and gallery slip joint(s) 48. Topside slip joint(s) 47, gallery slip joint(s) 48 or both may be positioned to allow for differential movement of casings 43, 44, 45. The clearance between product casing 43 and water jacket casing 45 of the lower slip joint(s) 48 may be exaggerated to allow for excess coolant to enter product gallery 40 at the inlet to product casing 43 so as to limit the thermal stress on product casing 43 when the temperatures of reaction product gases 49 a might exceed the material properties of the pipe used to form product casing 43. Excess coolant through joint 48 into cavity 40 can provide cooling of the reaction cavity roof (cap rock) and also treatment of the product gas to provide a thermal quench, chemical quench, and particulate removal. Product casing 43 and steam jacket casing 44 may be allowed to expand independently and/or at different rates of thermal expansion as compared to the external water jacket casing 45. In such a case, the entire production well assembly 42 may be drilled into the earth in a spiral pattern, or other conventional or unconventional pattern that would allow for the lateral support of internal free-floating casings, product casing 43 and steam jacket casing 44. A spiral pattern would remove the entire production assembly 42 from a strictly vertical orientation, to an orientation that has some horizontal component. Product casing 43 and/or steam jacket casing 44 may have external lugs or spacers that provide vertical support to the inner casings, by resting on the non-vertical inner surface of an outer casing. For example, a lug or spacer attached to product casing 43 may rest on the inner surface of steam jacket casing 44. Likewise, a lug or spacer from steam jacket casing 44 may rest on water jacket casing 45. Thus, in embodiments, product casing 43 and/or steam jacket casing 44 comprise external lugs or spacers that maintain the casing(s) more or less concentric with external water jacket 45, while still allowing for differential thermal growth.

FIG. 5 a is a schematic of an electric torch 30 during use in gasification of a coal deposit 11 according to embodiments of the invention. FIG. 6 is a schematic of an electric torch 30 according to another embodiment of the invention. Electric torch 30 promotes the thermolysis of water according to reaction (1) hereinbelow. Electric torch 30 may be a transferred arc plasma torch, non-transferred arc plasma torch, self-stabilized arc plasma torch, carbon arc plasma, or high temperature heater. In embodiments, electric torch 30 is selected from high temperature heaters, high temperature electrolyzers, lasers, and UV/catalytic systems. Preferably, electric device 30 comprises a steam plasma torch. Electric torch 30 is preferably water-cooled. Electric torch 30 creates its own steam moderator and oxygen for gasification near the point of reaction. Electric torch 30 may comprise more than one directional discharge head 55. Thus, more than one discharge head 55 may be used in a single reaction cavity 14. Electric torch 30 may be a mobile, directional electric torch, thus allowing the discharge 31 to be directed about axis 58 around rotatable joint 56, as discussed further hereinbelow.

FIG. 5 b is a schematic of an electric torch 30 during use in gasification of a coal deposit 11 according to an embodiment of the invention. By way of non-limiting example, three discharge heads 55 may be used. Two discharge heads 55 may be used in thin coal seams 11 where the directions of the electric discharge patterns (e.g., plasma arcs with steam) 31 are most beneficially opposed to each other and perpendicular to axis 58 of horizontal reaction shaft assembly 20. Where seams are thin, two horizontally opposed discharge heads 55 will extend the reach into the coal seam, in the direction perpendicular to axis 58, such that the electric torch 30 may gasify the maximum cross section of coal while traveling within horizontal reaction shaft assembly 20. This arrangement can provide a thin but wide cross section of coal removal. Electric torch 30 may comprise a plurality of discharge ports 55 and 55 a on a single device 30. In embodiments, the electric torch comprises two opposed discharge heads, in which the directional opposition is not parallel to centerline of the wellbore. The purpose of multiple ports is to produce jets of oxidant and/or moderator that may be ejected off-axis from the centerline of the well bore. This increases the width of the cavity by using the jet as a lance to cut the surface of the coal and to extend horizontally what is known in the art as the flame-front.

In embodiments, negatively and positively charged species are separated and expelled in separate directional jets shown as discharge heads 55 and 55 a and jets 31 and 31 a. In embodiments, oxidizer and reducers are separated and expelled in separate directional jets shown as discharge heads 55 and 55 a and jets 31 and 31 a. In embodiments, oxidant and moderator are separated and expelled in separate directional jets shown as discharge heads 55 and 55 a and jets 31 and 31 a.

In some embodiments, electric torch 30 creates a high-temperature discharge at a temperature of greater than about 2,000° F. (1093.3° C.). In certain embodiments, the plasma gas is produced at a temperature in the range of from about 8,000° F. (4426.6° C.) to about 16,000° F. (8871.1° C.). In some embodiments, the plasma gas is produced at a temperature of greater than about 8,000° F. (4426.6° C.). In embodiments, the plasma gas is heated to a temperature in excess of about 16,000° F. (8871.1° C.).

Where water is used as moderator, and steam as plasma gas, gasification system 10 may further comprise one or more means for creating and storing the initial charge of steam before initiation of the plasma, which can be for example, one or more electric immersion heaters and/or storage chambers may be used to create and store the initial charge of steam before initiation of the plasma. A start-up gas may also be transported from the surface via line 25, either in sufficient quantities for real-time needs, or in a smaller flow rate that may be stored in internal chambers in electric torch 30. Alternately, a storage of two separated chemical components may be stored in electric torch 30 such that the mixing of these chemical components may generate sufficient start-up gas.

As best illustrated in FIG. 6, electric torch 30 may comprise one or more moderator paths 38 which pass through the body of electric torch 30 and terminate in one or more annular nozzles (not shown) positioned along the circumference of the head(s) 55 of electric torch 30. Annular nozzles may be adapted to create moderator sprays 33 as shown in FIG. 6. Electric torch 30 may be sized relative to consumable casing 18 such that, when electric torch 30 is positioned within consumable casing 18, there exists a void or annular space 19 between electric torch 30 and consumable casing 18 such that fluid (for example, feed water 29, seal leakage water, etc.) may pass there through.

Referring to FIG. 5 a, electric torch 30 may carry umbilicals for supplying electrical power, plasma gas, start-up gas, moderator, oxidant, cavity coolant media, cooling water, or a combination thereof to the electric torch 30. Power is supplied to electric torch 30 via an umbilical 36 to electric torch 30 from surface 51. As shown in FIG. 3 b, umbilical 36 can comprise one or more conductors and/or grounds 34, which are surrounded by electrical insulation 35. Via this conductor, electrical current is carried to electric torch 30. Umbilical 36 comprises a retaining cable, or sheath, 24 or other means of mechanically communicating with electric torch 30 from earth surface 51. The retaining cable may envelop the conductor 34 which is insulated by electrical insulation 35. Retaining cable 24 may also act as a ground cable.

Bundled by the retaining cable 24 within umbilical 36 along with the insulated conductor may be a electric device cooling water supply line 23 to provide cooling water to electric torch 30, a plasma gas supply line 25 to provide initial plasma gas during start-up of electric torch 30, a moderator line 27 and/or an oxidant line 26 for supplying oxidant in addition to oxygen produced from injected water, should additional oxidant be desired. These lines may comprise flexible pipe, and may be surrounded by a further insulation layer within the retaining cable of umbilical 36. Desirably, following startup, only water and electricity are supplied to electric torch 30. In embodiments, a single surface-supplied commodity, exemplarily water, is provided to electric torch 30 as the electric torch 30 is operable to produce oxidant and moderator therefrom. The simplification of pumping only water into the injection well casing demonstrates the simplicity and economic benefits of the system design disclosed herein. Further benefit is derived by providing a system and method operable with a safe liquid (i.e. water) as opposed to conventional operation and systems which require utilization of hazardous gases such as substantially pure oxygen.

In general, gasifiers utilize three items in addition to fuel. These are (1) coolant to protect the hardware from damage, (2) steam as moderator for the carbon-steam reaction, and (3) oxygen to feed the partial-oxidation reaction. These reactions are further discussed hereinbelow.

Electric torch 30 may be a liquid cooled device. As shown in FIG. 3, in the preferred case where water is the common coolant and moderator, and steam the plasma gas, gasification system 10 may comprise cooling water and moderator line 28 through which water may be directly injected into injection well assembly 15 and, via communication, horizontal reaction shaft assembly 20.

Still referring to FIG. 3, in some embodiments, gasification system 10 comprises a single high pressure water feed 29 that is used for coolant, reactant, and oxygen source; and gasification system 10 comprises no lines bundled with the conductor encased in electrical insulation by umbilical 36. High pressure water feed 29 may comprise water at a pressure sufficient to overcome frictional flow losses, the differential pressure of the electric torch 30, and the static head of the product gases 49. Thus, multiple umbilicals are not needed for UCG, according to this disclosure. In embodiments, water may be introduced into injection well assembly 15 via cooling water and moderator line 28 at a rate sufficient to include allowances for extra steam to promote desirable reaction kinetics and for additional cooling. Electric torch 30 may use a plasma torch, electric heater, heat from the reaction cavity 14, or combinations thereof, to produce its own steam moderator from the heating of injected cooling water 28. As described further hereinbelow, some of the steam is processed through electric torch 30. Much of this steam is reduced to oxygen and hydrogen molecules, atoms, and ions by the extreme temperatures created in the torch, breaking the steam down into hydrogen and oxygen, providing oxygen source, plus free hydrogen for product gas 49. The heat produced via electric torch 30 significantly reduces the amount of oxygen required, such that the amount of oxidant provided by the torch discharge gas itself is sufficient and no further oxidant line is required. As discussed further hereinbelow, steam and oxygen react with carbonaceous deposit 11 (e.g., coal) to produce carbon monoxide and hydrogen, according to equations (2) and (3) hereinbelow. In preferred embodiments, electric torch 30 provides heat to create steam moderator, to provide required oxygen for the gasification reactions, and to produce a significant fraction of the hydrogen in raw syngas product gas 49.

Turning to FIG. 6, electric torch 30 may further comprise one or more boring bars, wedges, or casing splitters 39. In the event that consumable casing 18 does not completely erode during gasification, boring bar 39 or similar device is provided to remove or otherwise disable consumable casing 18 and expose further portions of coal deposit 11 to the heat of reaction cavity 14.

In embodiments in which a consumable casing is present, a casing material may be selected that is destroyed at high temperatures. Material having a degradation temperature higher than the saturation temperature of water in the coal, or more typically, higher than the pyrolysis temperature of the coal may be selected as the casing material in such embodiments. As device 30 is refracted, the consumable casing will erode and thus not interfere with the establishment of the cut of the coal, also described as advance of the flame front. Electric torch 30 is operable with water in the entire casing, in part to provide cooling of the casing, up to the point of the reaction. This ensures that the casing does not degrade prematurely, and that adequate water is delivered to electric torch 30 to prevent premature loss of water to the coal formation due to leakage.

Gasification system 10 may further comprise monitoring equipment (not shown). In embodiments, the monitoring equipment may be positioned within production well assembly 42, within horizontal reaction shaft assembly 20, above ground surface 51, or any combination thereof. The monitoring equipment may be adapted to analyze the product gas 49 and determine the BTU content, water content, opacity, temperature and/or mass flow rate thereof.

Turning to FIGS. 1 and 2, coal deposit 11 is prepared for gasification by the drilling of an injection well assembly 15 from ground surface 51 downward to the coal seam 11 which is to be gasified. The injection well may be fully lined with casing from the ground surface 51 to the bottom 59 of overburden 13, or further into coal deposit 11.

Production well assembly 42 is also prepared by the drilling of a bore from ground surface 51 downward to coal seam 11 which is to be gasified. The production well assembly 42 may be fully lined with casing 43 from ground surface 51 to the bottom 59 of overburden 13, or further into coal deposit 11 to be gasified.

Using directional drilling techniques which are well known, drilling is steered through a radius injection bore 22 into a horizontal reaction shaft assembly 20 whose path is substantially parallel with the coal seam 11 to be gasified. In embodiments, horizontal reaction shaft assembly 20 is substantially horizontal. In other embodiments, horizontal reaction shaft assembly 20 diverges from horizontal by up to 85 degrees. For example, in the case of steeply dipping beds, the divergence of horizontal reaction shaft assembly 20 from horizontal may approach 75 degrees or more. In certain embodiments, several horizontal reaction shaft assemblies 20 spaced in an array are drilled through into carbon deposit 11 to be gasified.

FIG. 7 is a plan view of one of several possible arrays 200 for the positioning of injection well assembly 15, horizontal reaction shaft assembly 20 and production well assembly 42 in a typical coal deposit 11 to be gasified. In embodiments, multiple electric torches 30 may be used to gasify coal deposits surrounding multiple horizontal reaction shaft assemblies 20 simultaneously. In other embodiments, portions of the coal deposit surrounding multiple horizontal reaction shafts 20 are gasified in series, using one or more electric torches 30. Reaction cavities 14 are illustrated after gasification, feeding common product gallery 40. Reaction cavities 14 are voids in the coal structure left after gasification. Multiple reaction cavities 14 may be created after several gasification operations in the coal structure, and such cavities may result in a radial or parallel pattern. As illustrated, horizontal reaction shaft assemblies 20 may be spaced so that pillars 50 consisting of solid and some devolatilized coal remain between the shafts following gasification. Since gasification of the coal weakens the ability of the deposit 11 to support overburden 13, walls or pillars 50 may be left behind for support. The diameter of reaction cavities 14 remaining after gasification will vary with the composition of coal deposit 11 and with the amount of heat supplied; the distance maintained between adjacent horizontal reaction shaft assemblies 20 during drilling should be determined accordingly to provide sufficient support. The thickness of overburden 13 and the thicknesses of the interspersed non-coal layers 12 are also relevant factors in determining the amount of pillar support, if any, which should be left behind. In some circumstances, no pillar support 50 is left behind, allowing for the potential collapse of overlying strata. In embodiments, the drilling pattern 200 may be similar to those patterns compatible with the Controlled-Retraction Injection-Point (CRIP) pattern described by Lawrence Livermore National Laboratory, and known to those of skill in the art.

In certain embodiments, the drilling pattern 200 may be similar to parallel horizontal injection and production shafts used to gasify steeply dipping coal beds, as known to those of skill in the art.

Thus, in embodiments, walls or pillars 50 of non-reacted or devolatilized coal may be left behind between the completed reaction cavities 14 to prevent roof spalling, cave-in, or surface subsidence. The rate of heat addition and moderator addition may be adjusted during gasification to minimize residual stresses in overburden 13 and the nearby walls or pillars 50. Further, high heat may be used to glaze the walls of reaction cavities 14 to provide further support and prevention of water in-leakage or product leakage. The directionality of electric torch 30 allows the operator to determine the size of the reaction cavity or cavities 14, as well as the cross-sectional shape or shapes thereof. The positive control of electric torch 30 also allows reaction cavities 14 to traverse any faults or geological inclusions in coal seam(s) 11.

Electric torch 30 may also be used as the means of drilling the various wells and shafts, if there is a line that returns to the surface that will remove product gas from the destruction of overburden 13 or coal seam(s) 11. Otherwise, a standard drilling apparatus or rig could be used for establishing the initial wells and shafts, as known to those of skill in the art.

As best described with reference to FIGS. 5 and 6, once the injection well assembly 15, the horizontal reaction shaft 20 and production well assemblies 42 are created, electric torch 30 is driven into horizontal reaction shaft assembly 20 through consumable casing 18. Electric torch 30 is adapted for horizontal movement within horizontal reaction shaft assembly 20 so that it may be positioned a desired distance for reaction with coal deposit 11.

In some embodiments, when the horizontal reaction shaft or shafts 20 have been established in the coal seam(s) 11, with communication to the production well or wells 42, then electric torch 30 is moved into position at the furthest production end of horizontal reaction shaft assembly 20 (i.e. the position within horizontal reaction shaft assembly 20 in closest proximity to production well assembly 42). At that time, electric torch 30 is initiated and gasification begun. Concurrently, cooling media and/or moderator may be injected into the growing horizontal reaction cavity 14, for example via cooling water and moderator path 38 in FIG. 6. Where water is used as moderator, and steam as discharge gas, electric heaters or storage chambers at electric torch 30 may create and store the initial charge of steam before initiation of the plasma. In other embodiments, a start-up gas line within umbilical 36 may be used to provide start-up gas for initiation of electric torch 30, a moderator line bundled within umbilical 36 may be used to provide moderator during initiation, and/or an oxidant line bundled within umbilical 36 may be used to provide oxidant during initiation of the electric torch 30.

In other embodiments, when the horizontal reaction shaft or shafts 20 have been established in the coal seam(s) 11, with communication to the production well or wells 42, then electric torch 30 is moved into position at the injection end of horizontal reaction shaft assembly 20 (i.e. the position within horizontal reaction shaft assembly 20 in closest proximity to injection well assembly 15). At that time, electric torch 30 is initiated and gasification performed substantially as described above.

In embodiments, electric torch 30 uses a plasma gas to complete the electrical path between the electrodes of electric torch 30. In most electric torches, such plasma gas would be an inert gas such as argon or nitrogen. However, by the disclosed method, a fluid such as steam and/or carbon dioxide may be employed as plasma gas, so that once ionized to the plasma state the gas provides reactive oxygen to reaction zone 32. Accordingly, the amount of electrical power provided to electric torch 30 not only provides heat but also, in this case, supplies oxygen as a reactant. If steam is used as plasma gas, hydrogen is formed in addition to oxygen. If carbon dioxide is used as a plasma gas, carbon ions or carbon monoxide is formed in addition to oxygen. If a solution of hydrogen peroxide or hydrazine is used as the plasma gas, then hydrogen is formed in addition to oxygen. At sufficiently high temperatures, water will spontaneously undergo direct thermolysis, the direct thermally-driven dissociation of water into hydrogen and oxygen molecules, according to reaction (1):

H₂O(g)→H₂(g)+½O₂(g)  (1)

At higher plasma temperatures, the molecules will break down further into ionized atoms. Additional hydrogen in product gas 49 is generally beneficial to the overall mix, depending on the desired usage of product gases 49. Direct thermolysis (thermally-driven dissociation of water) requires ultra-high temperatures, significantly greater than 2,000° F. (1093.3° C.) to begin the reaction, and greater than 8,000° F. (4426.6° C.) to drive the reaction to near-completion. These high temperatures present significant technical challenges for use within a traditional gasifier, as discussed hereinabove.

At temperatures above 8,000° F. (4426.6° C.), the Gibbs free energy, ΔG, (−RT In K) [where R is the gas constant, T is the absolute temperature and K is the equilibrium constant] becomes negative and the reaction may proceed spontaneously. The steam is thus heated past the point that ΔG becomes negative, so as to drive the complete break-down of water into hydrogen and oxygen according to reaction (1). The equilibrium constant equals (P_(H2) P_(O2) ^(1/2))/P_(H2O). Excess steam, for moderator and for cooling, assists in driving the reaction equilibrium towards formation of hydrogen and oxygen.

Although some materials of construction have melting points above 5,000° F. (2760° C.), for example tungsten, tantalum carbide, graphite, etc., it is generally unfeasible to operate at temperatures of greater than 6,750° F. (3732.2° C.). Thus, high temperature thermolysis in pressure-vessel reactors at elevated pressures is generally economically unfeasible. Using embodiments of the invention, gasification of coal deposits is performed by bringing the gasifier to the coal deposits, thus avoiding the problem of creating a pressure-vessel durable enough for thermolysis of water at high temperatures and/or high pressures.

The heat from discharge gas 31 first causes the volatiles to be stripped from the surrounding coal. This devolatilization may result in a cracking or fracturing of the coal, thereby increasing its permeability. The devolatilization and fracturing expands radially outwardly as heat front emanates from horizontal product shaft assembly 20 into the growing horizontal reaction cavity 14. The increased permeability of the devolatilized coal allows steam to flow outwardly into coal seam 11 for reacting with the fixed carbon. The discharge gas 31 and moderator spray 33 (e.g., steam) are preferably sprayed towards the walls of reaction cavity 14 at high pressure by means of one or more annular nozzles located around electric torch 30, as shown in FIG. 6. The one or more annular nozzles located around electric torch 30 may communicate with one or more passage lines 38 for providing moderator to reaction cavity 14. In the case where water is used as the moderator, then water may be the single liquid feed to electric torch 30, performing both moderator and coolant functions. By this method, the pumping of high pressure oxygen downhole, which is a hazardous operation, is not required.

Steam serves as a moderator reactant to gasify the fixed carbon component of the coal and favors the following water shift reactions:

i. C+H₂O+heat→H₂+CO  (2)

ii. 2C+2H₂O+heat→CH₄+CO₂  (3)

iii. CO+H₂O→H₂+CO₂+heat.  (4)

High temperature tends to favor reaction (2) and the production of H₂ and CO, while lower temperatures (nominally less than 2,372° F. (1300° C.)) tend to favor reaction (3) and the production of CH₄ and CO₂. High quality synthesis gas comprises less CH₄ and CO₂, and thus the production of high quality synthesis gas is favored by the utilization of electric torch 30 and high temperatures. At bulk reaction temperatures greater than approximately 2,700° F. (˜1500° C.), gasification will run clean, with a raw synthesis product gas 49 comprising primarily hydrogen and carbon monoxide, and with only a minimal percentage of less desirable carbon dioxide or methane. At these bulk reaction temperatures, greater than approximately 1,472° F. (800° C.), survival of ‘aromatic’ or ‘BTX’ (benzene, toluene, xylene) pollutants (also known as tars and phenol) is not possible, unlike in lower temperature UCG processes. Production of these unreacted heavier hydrocarbons will lead to the substantially complete destruction thereof in the high-temperature reaction zone 32.

In embodiments, excess steam is utilized for cooling purposes and also for the carbon-steam reaction (2). Excess steam may also promote reaction (4). Excess steam serves to discourage recombination of hydrogen and oxygen into water (lowers the partial pressures of hydrogen and oxygen relative to partial pressure of steam). This is desirable so that oxygen is available for reaction with carbon atoms from the coal. Seal leakage water may leak into an annular sealing space 19 between electric torch 30 and consumable casing 18. This water acts as a coolant to both consumable casing 18 and the outside of electric torch 30. Water that escapes into reaction cavity 14 will become steam and will act as a moderator to the process and/or as coolant of reaction cavity 14 as a thermal quench or chemical quench.

Because low reaction temperature favors the production of CH₄ and CO₂, while higher temperatures favor the production of CO and H₂, the temperatures in reaction zone 32 and horizontal reaction cavity 14 can be estimated in part by the composition of product gas 49. Further, the temperatures of reaction zone 32 and horizontal reaction cavity 14 may be modulated to attain the desired mixture of gases within product gas stream 49. Temperature may be modulated by many methods, including, but not limited to, variance of the power to electric torch 30, change in the flow of fluid 29, and the speed of withdrawal or advancement of electric torch 30 within horizontal reaction shaft assembly 20. Such modulation may be time-dependent. For example, in some embodiments, lower temperature may be provided at the virgin coal seam 11 to favor pyrolysis, perhaps with CH₄ and CO₂ production, and subsequently the temperature of reaction zone 32 is raised to favor reaction of the devolatilized carbon into synthesis gas components, CO and H₂.

The product gases 49 a produced by devolatilization and gasification reactions move toward common product gallery 40 and production well assembly 42 for removal. In embodiments, as coal deposit 11 is gasified, electric torch 30 is positioned closer to injection well assembly 15 by moving electric torch 30, in embodiments by withdrawing umbilical 36, along the direction of travel indicated by arrow 52 in FIG. 1. In embodiments, electric torch 30 is continuously withdrawn through horizontal reaction shaft assembly 20. In other embodiments, electric torch 30 is intermittently repositioned within horizontal reaction shaft assembly 20. As shown in FIG. 1, electric torch 30 may be withdrawn in a generally horizontal path in the direction indicated by arrow 52 through the coal deposit 11 to be gasified.

In alternative embodiments, electric torch 30 is originally positioned near the injection end of horizontal reaction shaft assembly 20 and advanced in the direction indicated by arrow 52 a from the injection end of horizontal reaction shaft assembly 20 towards the production end of horizontal reaction shaft assembly 20 during gasification. In such embodiments, electric torch 30 may be pushed in a forward direction, i.e. the direction indicated by directional arrow 52 a, as gasification of coal deposit 11 proceeds.

Electric torch 30 provides intense heat to reaction zone 32. As such, it may be desirable to add a coolant media to reaction cavity 14 to temper the temperature near reaction zone 32, to temper the temperature of reaction cavity 14, to temper the heat to the cavity cap rock, and/or to temper the temperature of hot product gas 49 a prior to entering product gallery 40 and/or production well assembly 42. Ideally, such a coolant media is water, in either liquid or gaseous form. Such water or steam may be taken from the cooling media added to electric torch 30 that keeps the device from overheating, for example from cooling water and moderator path 38. Water in steam form creates superheated steam when in contact with the high temperature environment of reaction zone 32 via sensible heat transfer, while liquid water effects latent heat transfer through the flashing of liquid water to steam. In a supercritical environment, there may not be distinct water and steam phases, even though cooling is still taking place.

Electric torch 30 cooling water may be introduced through a torch cooling water supply line 23 bundled within umbilical 36, a moderator line 27 bundled within umbilical 36, and/or into consumable casing 18 via cooling water and moderator line 28. Steam is created by waste heat in electric torch 30, by heat from reaction cavity 14, and by flashing of water due to the high temperature of discharge gas 31 created by electric torch 30.

Supplemental oxygen or other oxidant may be added to reaction zone 32 to provide partial oxidation of the carbon. This reaction would add supplemental heat to reaction zone 32, which would lessen the amount of heat that would need to be added by means of electric torch 30. Such reactant could be pure oxygen, air, oxygen-enhanced air, hydrogen peroxide, aqueous solutions of oxidants, or a mixture thereof.

In preferred embodiments, water is the only fluid injected via injection well 15 following initiation of electric torch 30.

The heat of the plasma and the gasification reactions erodes consumable casing 18, creating/enlarging reaction cavity 14. In the event that consumable casing 18 does not completely erode, boring bar, wedge or casing splitter 39 or similar device removes or otherwise disables the non-eroded portions of consumable casing 18 during repositioning of electric torch 30 such that exposed but unreacted portions of coal deposit 11 are presented to the hot reaction cavity 14. In embodiments, the boring bar, wedge, or splitter 39 is held in a non-deployed position within the body of electric torch 30 when the electric torch is first introduced to horizontal reaction shaft 20; and then the boring bar, wedge or splitter 39 is deployed to a greater diameter than the diameter of consumable casing 18 during initiation of operation. Ash, or a slag of molten ash, flows downwardly to the bottom of horizontal reaction cavity 14. A significant portion of the trace mercury and trace heavy metals originally found in coal deposit 11 that is gasified will be sequestered in this glassy slag.

A monitoring station (not shown) may be provided for continuously monitoring the temperature, BTU value, gas fractional content, water content, opacity (ash content), and/or mass flow rate of the fuel product gas 49. Operating parameters, such as reactant and coolant injection rates, torch power, and/or the positioning of the torch(es) 30 may be controlled in response to the monitoring. The increased kinetic rate of gasification supplied by the electric torch 30 allows for faster feedback for determining the product parameters at surface 51.

Product gas 49 may be monitored to determine the BTU content, water content, opacity, temperature, mass flow rate, or a combination thereof. The monitoring may be continuous or intermittent. When electric torch 30 is not being repositioned within horizontal reaction shaft assembly 20 with sufficient speed, gasification in the immediate cavity area will be substantially complete, which will present itself as a change in monitored product mix. The monitoring operation may be used to control operating parameters such as coolant and moderator flow rates and device electrical power during the gasification process. Control of the power to electric torch 30, the rate of addition of reactants, and/or the rate of addition of coolant, allows the temperature within reaction zone 32, product gallery 40, and/or production well assembly 42 to be controlled, as well as the temperature and pressure within reaction cavity 14. This enables control of the composition of the product gas 49 produced, because different temperatures and/or pressures will create a product gas 49 of a different composition.

Electric torch 30 is slowly repositioned along horizontal reaction shaft assembly 20 to reveal unreacted coal to the hot reactants. With reference to FIG. 5 a, discharge gas 31 created by electric torch 30 may be directed at an angle from the withdrawal axis 58, and optionally, during gasification, discharge gas 31 may be rotated about withdrawal axis 58 by rotation of discharge head(s) 55 about rotatable joint 56. Alternately, the entire electric torch 30 may be rotated. The utilization of the coal deposit 11 is thereby improved by directing the discharge gas 31 towards unreacted sections of the carbon deposit 11.

In embodiments, discharge head 55 is oriented to swivel around central axis 58, such that discharge gas 31 transcribes an angular path about central axis 58. In embodiments, discharge head 55 is rotatable about central axis 58 in a circular fashion. As such, when the discharge head is angled away from axis 58, and electric torch 30 is both rotated about axis 58 via rotatable joint 56 and withdrawn along horizontal reaction shaft assembly 20, discharge gas 31 scribes a screw pattern in reaction cavity 14. Reaction cavity 14 may have a substantially oval shape, but this invention is not limited by the shape of the reaction cavity 14 produced by plasma gasification. By controlling the number of discharge heads 55, the path scribed by rotation thereof, and the rate of withdrawal or advancement of electric torch 30 within horizontal reaction shaft assembly 20, the shape of reaction cavity 14 may be controlled. In thin seams, the shape of the reaction cavity may be created as an elongated oval. This feature may enable the underground gasification of coal deposits 11 that have previously been considered too deep and/or too thin for other in situ technologies.

The initial heat from electric torch 30 causes a portion of the volatiles of the coal deposits 11 to be stripped off and, subsequently, with the reaction of moderator and oxidant, the remaining fixed carbon is gasified according to Equations (2) and (3), leaving behind ash and/or a slag of molten ash at the bottom of horizontal reaction shaft assembly 20. Upon complete gasification, the diameter of horizontal reaction shaft assembly 20 will have increased to the size of reaction cavity 14.

Via production well 42, hot product gases 49 a are lead from reaction cavity(ies) 14, and optionally product galleries 40, to the surface 51. As discussed further hereinabove, in order to keep product casing 43 from overheating, it may be desirable to use one or more concentric outer casings 44, 45 that are filled with cooling water and/or steam to create useful high-pressure steam 41 by heat transfer with hot product gas 49 a. At least a portion of high pressure steam 41 may be introduced into a steam turbine/condenser 53. Steam turbine/condenser 53 may produce electricity 54 to power electric torch 30. Additional electricity produced may be used on-site or sold for profit. Because of the high electric usage of electric torch(es) 30, an operator may choose to operate electric torch 30 only during off-peak electrical demand periods, storing up heat in the reaction cavity 14 until the following non-peak electrical demand period. This is also true for product and process compressor equipment (not shown) at earth surface 51.

Turning to FIGS. 4 and 7, hot product gases 49 a exit the production end of horizontal reaction shaft assembly 20, and enter product gallery 40 connecting several reaction cavities 14 or production well assembly 42. From product gallery 40, hot product gas 49 a enters production well assembly 42 and exits at surface 51 as product gas 49. Product gas 49 collected at the topside end of production well assembly 42 may undergo surface processing. Once product gas 49 are collected at surface 51, the product gas 49 may be upgraded to pipeline quality or used in any other way, as known to those of skill in the art.

Product gas 49 may comprise any type of gas or gases, in varying volumes. For example, product gas 49 may comprise synthesis gas. Product gas 49 may comprise greater than about 25 volume percent H₂. In embodiments, product gas stream 49 comprises about 45 volume percent H₂. Product gas 49 may comprise greater than about 25 volume percent CO. In embodiments, product gas stream 49 comprises about 45 volume percent CO. Product gas stream 49 may comprise less than about 25 volume percent CO₂. In embodiments, product gas stream 49 comprises less than about 5 volume percent CO₂. Product gas stream 49 may comprise less than about 50 volume percent H₂O. In embodiments, product gas stream 49 comprises less than about 8 volume percent H₂O. Product gas 49 may further comprise one or more components selected from methane, hydrogen cyanide, ammonia, nitrogen gas, hydrogen sulfide, carbonyl sulfide and others. Desirably, the amount of these components in product gas 49 is less than about 5 volume percent.

Product gas 49 may exit production well assembly 42 at a high pressure. Because the product gas 49 is at a high pressure, the need for capital-intensive gas compressors at surface 51 may be eliminated and/or reduced via the disclosed method. The pressure of product gas 49 may be greater than about 2000 psi (13,789.5 kPa). Alternatively, the pressure of product gas 49 may be greater than about 1500 psi (10,342.1 kPa). In other embodiments, the pressure of product gas 49 may be greater than about 1073 psi (7,398 kPa). In other embodiments, the pressure of product gas 49 may be greater than about 3,028 psi (22,120 kPa).

Product gas 49 comprising synthesis gas at high pressure may be utilized as known to those of skill in the art. Synthesis gas may be utilized for the production of synthetic fuels as is known to those of skill in the art. Hydrogen may be recovered from product gas 49 for use as a power fuel, for oil refineries, and for the chemical industry. Synthesis gas can be utilized, for example, to produce commodity chemicals such as, but not limited to, methanol, DME, diesel, jet fuel, gasoline, acetyl chemicals, ethanol, ammonia, and combinations thereof. Carbon dioxide in product gas 49 may be recovered and utilized for any means known to those of skill in the art. For example, carbon dioxide gas in product gas stream 49 may be utilized for enhanced oil recovery (EOR). For use in most EOR operations, carbon dioxide should have a pressure of greater than about 1500 psi. Because product gas stream 49 exits production well 42 at high pressure, the carbon dioxide gas in product stream 49 may, in some embodiments, be utilized for EOR without first being compressed.

The disclosed underground gasification system and method may be used to gasify about 40 ton/hour (40.64 tonne/hr) or more of coal deposit per horizontal reaction shaft assembly 20. Product gas 49 may be produced at greater than about 2,500 MCF (MCF=1000 cubic feet) (70,792 m³). In specific embodiments, product gas 49 may be produced at about 2,684 MCF (76,002 m³). Product gas 49 may comprise greater than 200 BTU/SCF HHV (41.8 kJ/m³). In embodiments, product gas 49 comprises about 318 BTU/SCF HHV (66.5 kJ/m³). Product gas 49 may comprise greater than 250 BTU/SCF LHV (52.3 kJ/m³). In embodiments, product gas 49 comprises about 290 BTU/SCF LHV (60.6 kJ/m³). Product gas 49 may be produced at more than about 600 MMBTU/h (633,034 MJ/h). Product gas 49 may be produced at more than about 700 MMBTU/h (738,539 MJ/h). In some specific embodiments, product gas 49 may is produced at about 789 MMBTU/h (832,439 MJ/h) of chemical energy, net of thermal or kinetic energy.

The disclosed system and method eliminates traditional mining costs, transportation costs, strip mining, and underground personnel by “mining” coal out of the ground by gasifying it and bringing energy to the surface 51. The disclosed systems and methods enable very deep operation, with long horizontal reaction shaft assemblies, rather than shallow wells and close well centers, typical with traditional UCG, which are more disruptive to the environment. Via the disclosed system(s) and method(s), the electric device/torch 30 may be directional and the temperature, pressure, and reaction rates may be adjusted to alter the composition of product gas 49. Traditional UCG methods are passive air or oxygen injection methods, which do not allow for control over the shape of reaction cavity 14 or substantial control of reaction temperatures.

Via the disclosed system and method, synthesis gas-comprising product gas 49 may be produced for less than the cost of synthesis gas from traditional gasifiers. For example, synthesis gas 49 may be produced at less than about $2.00/mmBTU ($1.89 per GJ) at the head of production well 42. In embodiments, electric torch 30 utilizes about 1 MW of electricity 54, and this may be supplied via steam turbine/condenser 53 or other power sources. In embodiments, electric torch 30 utilizes about 10 MW of electricity 54, and this may be supplied via steam turbine/condenser 53 or other power sources. The amount of energy consumed by electric torch 30 may be about 5%-25% of the gross energy of the gasification reactions.

While preferred embodiments of this invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit or teaching of this invention. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the system and apparatus are possible and are within the scope of the invention. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims which follow, the scope of which shall include all equivalents of the subject matter of the claims. 

1. A system for the gasification of a coal deposit located below the ground surface, the system comprising: an injection well assembly comprising one end positioned proximate the ground surface and the opposite end of the injection well assembly located adjacent to or within the coal deposit; a production well assembly comprising one end positioned proximate the ground surface and the opposite end of the production well assembly located adjacent to or within the coal deposit; a non-vertical reaction shaft assembly located adjacent to or within the coal deposit a distance below the ground surface, the non-vertical reaction shaft having a length and comprising an injection end in communication with the end of the injection well assembly located adjacent to or within the coal deposit and a production end in communication with the end of the production well assembly located adjacent to or within the coal deposit; and an electric torch configured to move within the non-vertical reaction shaft assembly and create an oxidant and moderator downhole.
 2. The system of claim 1 wherein the coal deposit comprises at least one selected from the group consisting of peat, lignite, sub bituminous coal, bituminous coal, anthracite, and combinations thereof.
 3. The system of claim 1 wherein the injection well assembly is within 15 degrees of vertical.
 4. The system of claim 1 wherein the non-vertical reaction shaft assembly diverges from vertical by more than 15 degrees.
 5. The system of claim 1 wherein the electric torch comprises a non-transferred arc plasma torch, and wherein the electric torch utilizes steam as the plasma gas.
 6. The system of claim 1 wherein the electric torch comprises one or more directional jets which may be actively or passively vectored to shape a reaction cavity.
 7. The system of claim 6 wherein the electric torch is operable to separate positively charged species from negatively charged species or is operable to separate oxidizers from reducers or both and wherein the electric torch is configured to expel separate jets thereof.
 8. The system of claim 1 wherein the non-vertical reaction shaft is at least partially lined by a water-cooled, thermally-consumable casing material.
 9. The system of claim 1 wherein the distance below ground surface is greater than about 3,000 feet (914.4 m).
 10. The system of claim 1 wherein the only fluid inlet into the system is one or more inlets for liquid water or liquid carbon dioxide.
 11. The system of claim 1 wherein the production well assembly further comprises a product casing, a steam jacket casing surrounding at least a portion of the product casing, and an external water jacket casing surrounding at least a portion of the steam jacket casing, wherein the external water jacket casing comprises an inlet for water and wherein the steam jacket casing comprises an outlet for steam and wherein the product casing transfers product gasification gas from the non-vertical reaction shaft assembly to the surface.
 12. The system of claim 11 wherein at least one of the steam jacket casing and the product casing is capable of expanding independently and/or at different rates of thermal expansion as compared to the external water jacket casing.
 13. A method for gasifying a coal deposit located below the ground surface, the method comprising: positioning an electric torch comprising a discharge head within a non-vertical reaction shaft assembly, the non-vertical reaction shaft assembly having a length, an injection end, and a production end, and wherein the non-vertical reaction shaft assembly is positioned at least partially within the coal deposit a distance of at least 1,000 feet (304.8 m) below ground; and internally creating, with the electric torch, an oxidant and a moderator from an externally-supplied liquid, whereby at least a portion of the coal deposit is gasified to create a reaction cavity, wherein the electric torch is operated at a temperature.
 14. The method of claim 13 wherein the coal deposit comprises at least one selected from the group consisting of peat, lignite, sub bituminous coal, bituminous coal, anthracite, and combinations thereof.
 15. The method of claim 13 wherein the electric torch is attached to one end of each of at least one retaining cables whereby each of the at least one retaining cables extends from the electric torch through an injection well to the ground surface; and wherein the production end of the non-vertical reaction shaft assembly is in communication with a below-ground end of a production well, and wherein the injection well comprises one end in communication with the ground surface and one end in communication with the injection end of the non-vertical reaction shaft assembly.
 16. The method of claim 13 wherein the production well further comprises: a product casing adapted to transfer product gasification gas from the non-vertical reaction shaft assembly to the surface; a steam jacket casing surrounding at least a portion of the product casing, the steam jacket casing having an outlet; and an external water jacket casing surrounding at least a portion of the steam jacket casing, the external water jacket casing having an inlet; and wherein the method further comprises injecting water into the inlet of the external water jacket casing and extracting steam from the outlet of the steam jacket casing.
 17. The method of claim 16 wherein at least one of the steam jacket casing and the product casing is capable of expanding independently and/or at a different rate of thermal expansion as compared to the water jacket casing.
 18. The system of claim 17 wherein at least one casing selected from the product casing and the steam jacket casing comprises spacers, whereby the at least one selected casing remains substantially concentric with the external water jacket casing during gasification of the coal deposit.
 19. The method of claim 13 wherein the non-vertical reaction shaft assembly diverges from vertical by more than 15 degrees.
 20. The method of claim 13 wherein the electric torch operates with steam as plasma gas.
 21. The method of claim 13 wherein the electric torch comprises one or more directional jets which may be actively or passively vectored to shape the reaction cavity.
 22. The system of claim 21 further comprising operating the electric torch to separate positively charged species from negatively charged species or to separate oxidizers from reducers or both and expelling separate directional jets thereof.
 23. The method of claim 13 wherein the distance below ground surface is greater than about 3,000 feet (914.4 m).
 24. The method of claim 13 wherein the externally-supplied liquid is water, which is utilized as coolant, reactant, and/or moderator during gasification, and from which the electric torch produces steam and oxygen for its operation.
 25. The method of claim 13 wherein water is the only fluid injected into the electric torch and the non-vertical reaction shaft assembly following startup. 